Field of the Invention
The invention relates to a safety device protecting against overpressure failure of a nuclear reactor pressure vessel due to overpressure in the event of insufficient core cooling.
A relief device for a pressure vessel is described in Australian Patent No. 18,171/67. The relief device includes a fusible plug which is fitted in such a way that it blocks a flow channel leading out of the pressure vessel. The plug is constructed in such a way that it is solid below a critical temperature and breaks up at the critical temperature.
If, in a nuclear power station in general and in a pressurized-water reactor nuclear power station in particular, the extremely improbable failure of all of the cooling devices of the reactor core is assumed, there is a risk of the reactor core being overheated. In a pressurized-water nuclear power station, an inadmissible overpressure in the primary circuit is avoided by the pressurizer system with spray devices and blow-off devices. A blow-off vessel serves to condense the steam blown off upon opening of the pressurizer valves, blow-off valves and relief valves and of the volume control system relief valves. The blow-off vessel is filled with water up to about two thirds, and above that is a nitrogen cushion. In pressurized-water reactors, the pressure in the primary circuit is, for example, 158 bar.
The invention starts from the consideration of substantially reducing the blow-off response pressure in a cooling circuit of a nuclear reactor, especially in the primary circuit of a pressurized-water reactor, as a function of temperature, in such a way that in the highly improbable case of overheating of the reactor core, the primary circuit pressure is automatically reduced to values below 30 bar.